1. Field of the Invention
The present invention relates to touch panels and, particularly, to a carbon nanotube based touch panel and a display device using the same.
2. Discussion of Related Art
Following the advancement in recent years of various electronic apparatuses, such as mobile phones, car navigation systems and the like, toward high performance and diversification, there has been continuous growth in the number of electronic apparatuses equipped with optically transparent touch panels at the front of their respective display devices (e.g., liquid crystal panels). A user of any such electronic apparatus operates it by pressing or touching the touch panel with a finger, a pen, a stylus, or another like tool while visually observing the display device through the touch panel. Therefore, a demand exists for touch panels that provide superior visibility and reliable operation.
Up to the present time, different types of touch panels, including resistance, capacitance, infrared, and surface sound-wave types have been developed. The capacitance-type touch panel has advantages such as higher accuracy and excellent transparency, and thus has been widely used.
There are two kinds of conventional capacitance-type touch panels: the single-point capacitance-type touch panel, and the multipoint capacitance-type touch panel. The multipoint capacitance-type touch panel includes a glass substrate, a plurality of transparent conductive layers, a capacitive sensing circuit, and a plurality of sense traces. The transparent conductive layers and the sense traces are separately disposed on a surface of the glass substrate. The transparent conductive layers are placed at different locations on the surface of the glass substrate. Each transparent conductive layer is electrically connected to the capacitive sensing circuit by a respective sense trace. The capacitive sensing circuit includes at least one integrated circuit recording positions of the transparent conductive layers. The material of the transparent conductive layers and the sense traces is selected from a group consisting of indium tin oxide (ITO) and antimony tin oxide (ATO). Additionally, a filling layer is formed in gaps between the adjacent transparent conductive layers and the adjacent sense traces. The material of the filling layer has a refractive index similar to the material of the transparent conductive layers. As such, the touch panel with the filling layer can provide uniform transparency. Further, a protective layer is formed on the surface of the transparent conductive layer that faces away from the substrate. The material of the protective layer has insulative and transparent characteristics.
In typical operation, an upper surface of the touch panel is pressed/touched with one or more touch tools simultaneously. The touch tools can for example be one or more fingers of a user or several users. Visual observation of a screen on the liquid crystal display device provided on a backside of the touch panel is provided. For example, in the case where a user touches the upper surface with two fingers simultaneously, due to an electrical field of the user, coupling capacitances form between the user's fingers and the transparent conductive layers. For high frequency electrical current, the coupled capacitances act as conductors, and thus the user's fingers take away currents from the touch points. Currents flowing through the capacitive sensing circuit cooperatively replace the currents lost at the touch points. Thus the positions of the touch points can be simultaneously identified by the integrated circuit of the capacitive sensing circuit.
The transparent conductive layers (e.g., ITO layers) are generally formed by means of ion-beam sputtering, and this method is relatively complicated. Furthermore, the ITO layers have generally poor mechanical durability, low chemical endurance, and uneven resistance over an entire area of the touch panel. Additionally, the ITO layers have relatively low transparency. All the above-mentioned problems of the ITO layers tend to yield a touch panel with relatively low sensitivity, accuracy, and brightness.
What is needed, therefore, is a touch panel having good durability, and providing high sensitivity, accuracy, and brightness. What is also needed is a display device using such touch panel.